The invention relates to a piecing device that is mobile along an open-end spinning machine and that can be sequentially presented to the individual assembles of the open-end spinning machine. Piecing devices of the type contemplated by the present invention include means for lifting off a spool from a drive element of the appurtenant spinning assembly and for driving the spool during the piecing operation, including an auxiliary roll that is applied to the spool and that is provided with a drive, and with means for guiding the yarn from and to the spool, comprising a pair of feed rolls with a drive, whose drive is attuned to the drive of the auxiliary roll.
In a known construction of this kind (German Offenlegungsschrift No. 2,361,787) there are difficulties in the running up phase, i.e. when the yarn applied to a sliver ring in a spinning rotor is once more to be drawn off from the spinning assembly and wound. The feed rolls, together with the practically massless yarn very rapidly reach the desired feed velocity, while the winding speed corresponding to this feed velocity is reached with a delay, due, at least partly, to the greater intertial masses involved. Particularly if the spool is relatively full, there is a slippage between the auxiliary roll and the spool, so that the auxiliary roll cannot accelerate the spool in a way corresponding to the acceleration of the delivery rolls with the yarn that is to be fed. In this delayed acceleration of the spool to its winding speed, the yarn tension drops between the pair of feed rolls and the spool in such a way that a loop of yarn is formed there. Because of the spinning twist given to the yarn this has the effect that in the region of the yarn loop the yarn will kink on itself and run to the spool as a kink. This kink on the spool can be very disturbingly noticeable in further processing.
In a known piecing device (German Offenlegungsschrift No. 2,008,142) there is an additional provision that during the piecing process the yarn will still run via the spool drive roll of the spinning assembly in question, which is driven at its normal operating rpm. Since the yarn is not clamped there, it cannot be predicted what effect the drive roll will have on the yarn. Here also there are difficulties in the running up phase, for the reasons that have been indicated, leading to kinking. Here also it is not possible to accelerate the spool in the same way as the pair of feed rolls, so that in this run up phase the yarn tension is removed and a loop is formed.
The invention is intended further to develop a piecing device of the described type which, even in the running up phase, i.e. when the pieced yarn is again to be drawn from the piecing device, it will be ensured that there will be a controlled yarn guiding and the formation of loops and kinks will be avoided. This problem is solved by contemplated embodiments of the invention, in that means are provided which can be supplementarily switched in to influence the course of the yarn in the region between the pair of feed rolls and the auxiliary roll and/or to influence the winding speed.
According to the invention, in many instances it will be sufficient if during the running up phase it be provided that no differences in speed can occur, while in many cases it will also suffice only to control the running of the yarn in the region between the pair of feed rolls and the auxiliary roll during the running up phase. In most cases however, and in the most preferred embodiments of the invention, it will be advantageous to undertake both measures simultaneously, i.e. to influence the increase in the winding speed and at the same time to provide an additional yarn guide during the running up phase.
In an advantageous embodiment of the invention, it is provided that the supplementary means are connected to a program control that controls the whole work sequence, which will determine the time of switching in and/or the duration of the switching in.
To accelerate the increase in winding speed so that the slippage between the auxiliary roll and the spool will be reduced, in a simple embodiment of the invention, a loading device is provided that presses the spool against the auxiliary roll during the running up phase.
In order, during the running up phase, to be able to influence the course of the yarn, a yarn storage device is disposed between the pair of feed rolls and the auxiliary roll, which storage device accepts the yarn that is fed but not wound during the running up phase, in case of differences between the feed velocity and the winding speed. Such a yarn storage device can be further exploited, in that it participates in the preparatory process by forming a yarn reserve which is released in the carrying back of the yarn into a spinning rotor, so that in this case the auxiliary roll no longer needs to be driven against the drawoff device, shortly before the running up phase.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, several embodiments in accordance with the present invention.